The invention relates to a current-source arrangement for generating a current which is substantially temperature-independent or has a negative temperature-dependence, which arrangement comprises a current-stabilizing circuit for generating a current having a positive temperature-dependence.
Such a current-stabilizing arrangement is disclosed in U.S. Pat. No. 3,914,683. The arrangement comprises two parallel circuits between a first and a second common terminal. The first circuit comprises a first resistor, a first transistor and a second resistor and the second circuit comprises a second transistor and a third resistor. The first and the second transistor have common control electrodes which are driven by a differential amplifier whose control electrodes are connected to a point between the first transistor and the second resistor and a point between the second transistor and the third resistor.
The output current of such a current stabilizer is proportional to the ratio between the absolute temperature and the resistance of the first resistor. In accordance with the above-mentioned Patent this output current may be used for deriving a temperature-independent current or voltage, or a current or voltage with a positive or a negative temperature-coefficient.
A current with a positive temperature dependence is required, for example, in an integrated FM receiver as described in the non-prepublished European Patent Application No. 83200281. In such a receiver, low-pass filters are employed for tuning and for frequency-to-phase converters for, inter alia, demodulation. In order to ensure operation over a wide temperature range, the receiver should meet stringent requirements. In order to minimize the effect of temperature variations it is necessary to employ temperature-compensated transconductance filters in the tuning section and, if delay elements are employed in the frequency-to-phase converters, temperature-compensated delay elements. Such delay elements are the subject of U.S. patent application Ser. No. 590,095 filed simultaneously with the present Application.
A stabilized current which is directly proportional to the temperature of the integrated circuit is required for the temperature compensation of the transconductance filters. Such a current can be generated with the current-stabilizing arrangement described in said United States Patent, the first resistor being externally added to the integrated circuit so as to prevent the temperature dependence from being influenced.
Both a temperature-independent voltage and a temperature-independent current are needed for the temperature compensation of the delay elements. A temperature-independent voltage can be obtained by means of a fully integrated current stabilizer in accordance with said United States Patent. However, the known current-stabilizing arrangement can supply a temperature-independent current only if an external resistor is added to the integrated circuit.
The temperature compensation of both the transconductance filters and the delay elements then requires the use of two current-stabilizing arrangements each with an externally added resistor and hence two connection pins on the integrated circuit. This entails additional costs and makes it more difficult to obtain an integrated FM receiver of the desired small dimensions.